| From: | Darren Duncan <darren(at)darrenduncan(dot)net> |
|---|---|
| To: | pgsql-general(at)postgresql(dot)org |
| Cc: | Kevin Jardine <kevinjardine(at)yahoo(dot)com> |
| Subject: | Re: Preserving order through an inner join |
| Date: | 2010-09-27 19:04:40 |
| Message-ID: | 4CA0EAC8.5080409@darrenduncan.net |
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| Lists: | pgsql-general |
Gurjeet Singh wrote:
> On Sun, Sep 26, 2010 at 9:37 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> The SQL standard explicitly disavows any particular
> output row order unless there is a top-level ORDER BY. (In fact,
> unless things have changed recently an ORDER BY in a sub-select isn't
> even legal per spec.)
>
> Not sure about the SQL spec allowing it, but an ORDER BY followed by a
> LIMIT does have valid use cases in sub-selects.
Absolutely it does, but that is just a row *filtering* operation. You still
have to have a separate ORDER BY in the outermost query to get result rows
output in a particular order. -- Darren Duncan
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